4. Research questions and projects
- What are the risks of ATES systems on groundwater
quality (chemical, microbiological and physical)?
- Where can we allow what type of ATES systems?
Two research projects:
- Matthijs Bonte: hydrochemical impacts (BTO)
- Philip Visser: physical impacts (TTiW)
5. Approach and methods
- Monitoring ATES systems at 3 sites (mostly 7-17°C)
- Laboratory experiments (5-60°C)
- Numerical modelling (Modflow/Mt3D,Phreeqc)
7. Field ATES system – Eindhoven:
Monitoring program 2005-2012 (Brabant Water)
Key question: what effects are visible at field scale?
Drinking water
ATES site Pumping station
8. Field data – Eindhoven
Depth profiles of ambient groundwater quality
-ATES system is realized in
Sterksel aquifer
-Vertical redox zonation:
removal of NO3, SO4;
followed by appearance of
CH4
11. Laboratory investigations
Aim:
- Detailed analyses of
Hydrochemical changes
-Investigate more extreme T
- Investigate reaction
kinetics at different
temperatures
12. Types of lab experiments
-Test 1: Continuous flow test with 1 day residence time at 5,11,25 and 60ºC
in three sediment samples from the Sterksel formation
focus equilibrium reaction (sorption, mineral interaction)
-Test 2: Incubation test with increasing residence time (1-35d)
focus kinetically restricted (redox) reactions
-Text 3: Temperature ramping test with 5d residence (T = 5 to 80ºC)
focus kinetically restricted (redox) reactions
13. Collection of soil cores
-Percussion drilling
-Ackerman coring
-Working water sparged with N2
-Transport in N2 filled cooling box
16. Results of 1 day leaching test: comparing
concentration at 5, 25 and 60ºC with 11ºC
Leaching behavior Geochemical Temperature level
5ºC 25ºC 60ºC
Organic matter
Substances significantly Substance present in As DOC, P Silicates
thermally sediment K, Si Trace elements
influenced (p<0.01) in all three As, Mo, V
experiments,
Substance not present in Be
sediment above
detection limit
Not analysed F, Li
17. Results of 1 day leaching test: comparing
concentration at 5, 25 and 60ºC with 11ºC
Leaching behavior Geochemical Temperature level
5ºC 25ºC 60ºC
Organic matter
Substances significantly Substance present in As DOC, P Silicates
thermally sediment K, Si Trace elements
influenced (p<0.01) in all three As, Mo, V
experiments,
Substance not present in Be
sediment above
detection limit
Not analysed F, Li
Leaching behavior not Substance present in Alkalinity, SO4, Na, Mg, Sr, Ca, Fe, Mn, Al, Ba, Co, Cr,
significantly sediment Cu, Eu, Ho, Ni, Pb, Sb, Sc, U, Yb, Zn
influenced by temperature in all
three experiments
Substance not present in Ag, Bi, Cd
sediment
Not analysed Br, Cl, B, In, Tl
Substance below detection Substance present in Ga, La, Th
limit in reference and testing sediment
temperature
Substance not present in Bi, Se
sediment
18. Most relevant for drinking water: Arsenic
(but also in B, Mo, P)
Arsenic concentration as function of temperature
0.1
Mechanism (oxy)anion desorption
0.09
from Fe-oxides due to
0.08
- primarily temperature increase
Dissolved As (mg/l)
0.07
0.06
0.05 - DOC and P release (competition
0.04
for sorption sites)
0.03
0.02 Exp A
Exp B, Fe=3.2mg/l
0.01
Exp B, Fe=0.8mg/l
0 Exp C
0 10 20 30 40 50 60 70 Norm WLB
T(degC)
19. Arsenic sorption: described with Freundlich
sorption
and van ‘t Hoff equation
Sorption isotherm (Freundlich curve)
Q = KFC 1/ n
20. Sorption temperature dependence:
Van ‘t Hoff relation
Van ‘t Hoff plot
∆H ∆S
ln K d = +
RT R
ΔH points to Exothermic
sorption
(decreasing with T↑)
Literature range ~
-25 to -110kJ/mol
21. Field evidence of As and B leaching?
Heuvelgallerie Eindhoven (multiple
RIVM PB437-2
MWs)
0.04 13.5
30
13.1
0.035 25
12.7 20
[As] mg/l
T(ºC)
0.03
12.3 15
B (ug/l)
0.142x
y = 0.4323e
0.025 2
11.9
R = 0.5273
10
0.02 11.5 5
Aug-10 Nov-10 Feb-11 May-11 Sep-11 Dec-11 Mar-12 Jul-12
0
As Temp with data logger Manual T-readings 0 5 10 15 20 25
Temp (degC)
23. Temperature dependence of sulfate reduction
described with Arrhenius equation
Arrhenius equation:
Arrhenius plot SO4 reduction
4
3 Exp A
2 Exp B
Ln k (nmol/l/d)
1 Exp C
0 Linear
(Exp B)
-1 Linear
(Exp A)
-2 Linear
(Exp C)
Ea = 38-50 kJ/mol -3
Q10 = 1.7 - 2 -4
2.9 3.1 3.3 3.5 3.7 3.9
1000/T(1/K)
24. Results temperature ramping reveals
a ‘double peak’ pointing to 2 microbiological pop.
7
Effluent sulfate concentration (mg/l)
6
after 5 day residence time
5
4
3
2
1
0
0 10 20 30 40 50 60 70 80 90
T(°C)
Topt 1 Topt 2
25. Linear increase in dissolved organic carbon
but not in methane
4.0 60
CH4
3.5 50
3.0 40
DOC (mg/l)
DOC
CH4 (ug/l)
2.5
30
2.0
20
1.5
1.0 Influent DOC
10
0.5 0
Influent CH4
0.0 -10
0 20 40 60 80 100
T(°C)
-Biological methane production, no methane producers
at 70ºC?
-DOC shows no correlation with SO4 reduction rate
(DOC is often considered intermediate in Sulf.Red.)
28. PHREEQC modelling of 1-day residence time
column experiments
Key question:
-Can the inferred chemical processes explain the observed
quality trends
Processes included:
-Cation exchange
-Equilibrium with carbonate solid solution
-Kinetic dissolution of k-feldspar
-Surface complexation of trace elements to goethite
Model optimised with PEST (Marquardt-Levenberg method)
30. Modelling results: Si and K
Explained by incongruent K-feldspar dissolution
Decreasing rate with time due to
precipitation of secondary minerals
31. Modelling results: As, B, P, DOC, Mo
Expansion of PHREEQC / Dzombek & Morel
database with ΔH values for surface complexation
32. Conclusions PHREEQC modelling
Test results can be simulated with combination of cation exchange,
carbonate & K-feldspar dissolution and surface complexation
Constraint of the model is for some parameters quite poor, especially
surface complexation, e.g.:
ΔHAs = -38.5 ±13.3 kJ/mol (van ‘t Hoff plot: -42±2kJ/mol)
ΔHMo= -36.3 ± 32.2 kJ/mol
ΔHB = -14.9 ± 14.1kJ/mol (van ‘t Hoff plot: -22±4kJ/mol)
Due to high correlation between ΔH values (R2>0.8)
Surface complexation describes competition between species, different
parameters are closely linked
33. Conclusions: effects of ATES on water
quality
Field data:
-Mixing of vertical stratified
water qualities dominates
effects measured in field
-ATES induced mixing
potentially increases
vulnerability of phreatic
pumping stations
34. Conclusions: effects of ATES on water
quality
Field data: Laboratory data:
-Mixing of vertical stratified -Sorption of heavy metals is strongly
water qualities dominates temperature dependent (but probably
effects measured in field reversible)
-ATES induced mixing -Sulfate reduction rate breakdown
potentially increases in aquifers appears to follow
vulnerability of phreatic Arrhenius (Q10 1.7-2) but more
pumping stations temperature detail shows 2
maxima: ~40 and 70ºC
36. General conclusions
-ATES not in capture zone / protection zone’s of vulnerable
pumping stations
-In other area’s, impacts are probably acceptable and reversible
37. General conclusions
-ATES not in capture zone / protection zone’s of vulnerable
pumping stations
-In other area’s, impacts are probable acceptable and reversible
-At much higher temperatures (>25ºC), ATES
impacts reactive (buffering) capacity of aquifer (SOM degradation)
38. General conclusions
-ATES not in capture zone / protection zone’s of vulnerable
pumping stations
-In other area’s, impacts are probable acceptable and reversible
-At much higher temperatures (>25ºC), ATES drastically
impacts reactive (buffering) capacity of aquifer
-High T ATES is still an option, but only in aquifers where
irreversible impacts are acceptable (high salinity aquifers, high
vertical anisotropy)
